Php array sort by one value

Mastering PHP arrays: Array sorting

Sorting is an operation that arranges data in a specified way. PHP has several functions that deal with sorting arrays. Let’s examine these functions.

Good overview of sorting functions can be found in PHP manual: Sorting Arrays. All sorting functions act directly on an array variable itself because the variable is passed to sort function by reference, as opposed to returning a new sorted array. Because only variables can be passed by reference, you will get Fatal error when you try to pass array directly as a function argument.

Sort functions return true on success or false and warning message when parameter type differs from array.

 1php  2  3$array = [14, 1, 22, 8, 7];  4$return = sort($array);  5var_dump($return); // bool(true)  6  7$string = 'bar';  8$return = sort($string);  9Warning: sort() expects parameter 1 to be array, string given in php shell code on line 1 10var_dump($return); // bool(false) 

If two array members are evaluated as equal then the order is undefined. It’s unknown which number 1 will be at $array[0] or $array[1] :

1php 2 3$array = [3, 1, 2, 1]; 4sort($array); 

Most PHP sorting functions uses implementation of Quicksort.

Sorting single arrays

The simplest of sorting functions is sort, which sorts an array by its values from lowest to highest and doesn’t maintain the key association.

Modified sort functions offer also sorting by key (ksort), key-value association (asort), reverse sorting (rsort), user-defined comparison function (usort) and different variations of these functions. (arsort, krsort, uksort, ursort). There’s no reverse sorting version of user-defined sorting functions because reverse sorting can be performed by updating comparison rules.

Be careful when sorting arrays with mixed types of values because the sort function can produce unpredictable results. This also applies to sort functions with sort flag different to SORT_REGULAR, which is default sort flag for most sorting functions.

Example array with various types of scalar values:

 1php  2  3$array = [  4 true,  5 false,  6 'Hello',  7 'hi',  8 50,  9 0.25, 10 '4', 11 'hello', 12 '045', 13 '03', 14 'ABC', 15 "\x41", // hexadecimal ASCII code for letter 'A' 16 0x17, // hexadecimal representation of number 23 17 020, // octal representation of number 16 18 ]; 

Output of the sort($array) function for various sort flags will be:

As you can see sorted array differs for each sort flag. Comparison of sorted keys and values is case sensitive by default. For case-insensitive comparison, SORT_FLAG_CASE combination with SORT_STRING or SORT_NATURAL can be used.

1php 2 3$oranges = ['Orange1', 'orange3', 'orange1','Orange4']; 4 5sort($oranges, SORT_STRING); 6var_dump($oranges); 7 8sort($oranges, SORT_STRING | SORT_FLAG_CASE); 9var_dump($oranges); 

For natural ordering the natsort function and for the case-insensitive version the natcasesort function can be used. These functions are shortcuts for sort function with SORT_FLAG_CASE for case-sensitive version and SORT_FLAG_CASE | SORT_FLAG_CASE for case insensitive version. Natural ordering is using Natural Order String Comparison which is more human-friendly then a byte-by-byte comparison of sort function.

Other sorting options

Sort functions, with user-defined comparison function, give you an option to create a custom comparison function. User-defined comparison function sort family accept callback functions as a parameter. Callback functions can be simple functions, but also object methods, including static class methods and anonymous functions.

Sort function expects integer as a return value and all returning non-integer values are cast to an integer.

This behaviour is called type juggling and you can read more about it in PHP Manual: Type Juggling

Expected compare function return values:

• $first_compared_value == $second_compared_value => integer equal to zero; 0
• $first_compared_value < $second_compared_value =>integer less then zero; e.g -1
• $first_compared_value > $second_compared_value => integer greater than zero; e.g 1

Example: Interpolation of sort function with SORT_STRING sort flag using anonymous function/closure.

1php 2 3$array = ['Hello', 'Ahoy','Hi', 'hello']; 4 5usort($array, function($a, $b)  6 return strcmp($a, $b); 7>); 8 9var_dump($array); 

The output of this script will be:

It is possible to create a comparison function like this, because strcmp() function returns values as an usort() expectation defined earlier ( < 0 if str1 is less than str2; >0 if str1 is greater than str2, and 0 if they are equal).

Example: Sort by occurrence of character ‘o’:

 1php  2  3$array = ['Hello World', 'Ahoy','Hi'];  4  5function occurrenceOfO($a, $b)  6  7 $a_o_count = substr_count($a, 'o');  8 $b_o_count = substr_count($b, 'o');  9 10 if ($a_o_count === $b_o_count)  11 return 0; 12 > 13 14 return $a_o_count >= $b_o_count; 15> 16 17usort($array, 'occurrenceOfO'); 18var_dump($array); 

This outputs the following:

As you can see the usort function gives you an option to create complex sorting functions. Note that this function doesn’t maintain key-value association and assigns new keys to elements. If you want to maintain association use uasort function instead.

PHP 7 introduced three-way comparison operator ( ), also known as the “spaceship operator”, which has similar behaviour to the strcmp() function. This makes easier to write callbacks for comparison functions and return correct values expected by this function.

Example of spaceship operator behaviour:

1php 2 3echo 1 1; // 0 4 echo 1 2; // -1 5 echo 2 1; // 1 

Sorting multi-arrays

For sorting multiple or multi-dimensional arrays the array_multisort function can be used. This function works more like database style sorting — ‘ORDER BY’ multiple columns statement in SQL query, rather than a sort function which excepts multiple arrays and sorts these arrays independently.

 1php  2  3$magazine[] = ['year' => 2015, 'month' => 1, 'issue' => 1];  4$magazine[] = ['year' => 2014, 'month' => 12, 'issue' => 4];  5$magazine[] = ['year' => 2015, 'month' => 2, 'issue' => 2];  6$magazine[] = ['year' => 2015, 'month' => 3, 'issue' => 3];  7$magazine[] = ['year' => 2015, 'month' => 1, 'issue' => 2];  8  9var_dump($magazine); 10array_multisort($magazine); 11var_dump($magazine); 

The output of this script will be:

As you can see from outputted data, the array was sorted by year at first place, then by month and an issue number at last place.

Array shuffling

For randomizing the order of elements in an array the shuffle function can be used. This function doesn’t preserve key-value association and PHP doesn’t provide a built-in function for this.

The output of this script will differ on each call:

1php 2 3$numbers = [1, 2, 3, 4, 5]; 4shuffle($numbers); 5var_dump($numbers); 

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Sorting Arrays

PHP has several functions that deal with sorting arrays, and this document exists to help sort it all out.

• Some sort based on the array keys, whereas others by the values: $array[‘key’] = ‘value’;
• Whether or not the correlation between the keys and values are maintained after the sort, which may mean the keys are reset numerically (0,1,2 . )
• The order of the sort: alphabetical, ascending (low to high), descending (high to low), natural, random, or user defined
• Note: All of these sort functions act directly on the array variable itself, as opposed to returning a new sorted array
• If any of these sort functions evaluates two members as equal then they retain their original order. Prior to PHP 8.0.0, their order were undefined (the sorting was not stable).

Sorting function attributes

Function name	Sorts by	Maintains key association	Order of sort	Related functions
array_multisort()	value	string keys yes, int keys no	first array or sort options	array_walk()
asort()	value	yes	ascending	arsort()
arsort()	value	yes	descending	asort()
krsort()	key	yes	descending	ksort()
ksort()	key	yes	ascending	krsort()
natcasesort()	value	yes	natural, case insensitive	natsort()
natsort()	value	yes	natural	natcasesort()
rsort()	value	no	descending	sort()
shuffle()	value	no	random	array_rand()
sort()	value	no	ascending	rsort()
uasort()	value	yes	user defined	uksort()
uksort()	key	yes	user defined	uasort()
usort()	value	no	user defined	uasort()

User Contributed Notes 2 notes

While this may seem obvious, user-defined array sorting functions ( uksort(), uasort(), usort() ) will *not* be called if the array does not have *at least two values in it*.

function usortTest ( $a , $b ) var_dump ( $a );
var_dump ( $b );
return — 1 ;
>

$test = array( ‘val1’ );
usort ( $test , «usortTest» );

$test2 = array( ‘val2’ , ‘val3’ );
usort ( $test2 , «usortTest» );

The first array doesn’t get sent to the function.

Please, under no circumstance, place any logic that modifies values, or applies non-sorting business logic in these functions as they will not always be executed.

Another way to do a case case-insensitive sort by key would simply be:

uksort ( $array , ‘strcasecmp’ );
?>

Since strcasecmp is already predefined in php it saves you the trouble to actually write the comparison function yourself.

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PHP Sorting Arrays

The elements in an array can be sorted in alphabetical or numerical order, descending or ascending.

PHP — Sort Functions For Arrays

In this chapter, we will go through the following PHP array sort functions:

• sort() — sort arrays in ascending order
• rsort() — sort arrays in descending order
• asort() — sort associative arrays in ascending order, according to the value
• ksort() — sort associative arrays in ascending order, according to the key
• arsort() — sort associative arrays in descending order, according to the value
• krsort() — sort associative arrays in descending order, according to the key

Sort Array in Ascending Order — sort()

The following example sorts the elements of the $cars array in ascending alphabetical order:

Example

The following example sorts the elements of the $numbers array in ascending numerical order:

Example

Sort Array in Descending Order — rsort()

The following example sorts the elements of the $cars array in descending alphabetical order:

Example

The following example sorts the elements of the $numbers array in descending numerical order:

Example

Sort Array (Ascending Order), According to Value — asort()

The following example sorts an associative array in ascending order, according to the value:

Example

Sort Array (Ascending Order), According to Key — ksort()

The following example sorts an associative array in ascending order, according to the key:

Example

Sort Array (Descending Order), According to Value — arsort()

The following example sorts an associative array in descending order, according to the value:

Example

Sort Array (Descending Order), According to Key — krsort()

The following example sorts an associative array in descending order, according to the key:

Example

Complete PHP Array Reference

For a complete reference of all array functions, go to our complete PHP Array Reference.

The reference contains a brief description, and examples of use, for each function!

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